Therapeutic cancer vaccines are intended to drive specific activation of the immune system for therapy of existing malignancies or prevention of their recurrence. This requires powerful vaccination strategies, due to the preexisting immunosuppressive mechanisms orchestrated by the tumor. Theoretically, vaccination with apoptotic autologous tumor cells represents a particularly promising way to target the greatest number of potential antigens without the need for their individual identification. However, the sensing and clearance of apoptotic cells is generally considered to be a non-inflammatory or even tolerizing process. The prevailing view has been that apoptotic cells generated by normal tissue turnover are captured by dendritic cells (DCs) that migrate to local lymph nodes, where they induce T cell tolerance, T cell anergy, or T cell deletion in order to maintain tissue homeostasis and prevent autoimmunity in the host. We recently identified a novel DC subset (nDC), that, in contrast with other cross-presenting and cross-tolerizing DC subsets, potently (cross-)primes both CD4+ and CD8+T cells to cell-associated antigens after uptake of apoptotic material. The potent adjuvant activity of the nDC is largely dependent on their production of type I IFN after interacting with apoptotic cells. T cells primed by nDC display a greater capacity for primary expansion, cytokine production, and memory formation on a per cell basis than those primed by other DC subsets. As a consequence, these nDC are extremely potent in the induction of protective anti- tumor responses in both vaccination and therapeutic settings when exposed to apoptotic tumor cells. The central hypothesis underlying our proposed studies is that type I IFN production by nDC exposed to apoptotic cells is critical for nDC function and their subsequent priming of protective T cell responses to cell-associated antigens. The long-term goals of this work are two-fold: (1) definition of the molecular and cellular mechanisms in DCs that balance the pro- and anti-inflammatory immune response to self after cell death; and (2) translational exploitation of these mechanistic insights in order to devise effective therapeutic and preventive cancer vaccines. PUBLIC HEALTH RELEVANCE: Vaccination with apoptotic autologous tumor cells represents a particularly promising way to target the greatest number of potential antigens without the need for their individual identification. However, Cross- presentation of cell-associated antigens from apoptotic cells by DC generally leads to the induction of T cell tolerance. We have identified a new DC subset that is capable to prime T cells to cell associated antigen. In this project we will define the molecular and cellular mechanisms in these DCs that confer the T cell priming capacity in order to translational exploit of these mechanistic insights for the design of effective therapeutic and preventive cancer vaccines. .